In designing electrical and electronic systems, it is desirable to test the response of these systems to externally applied currents and electromagnetic fields which operate to induce currents within transmission lines in the systems. These systems may be exposed to potentially damaging currents and fields in actual use as a result of electrical storms, localized interference, or nuclear detonations, among other causes. The response of these systems to large electromagnetic pulses is therefore of significant concern since it is a common design goal to design systems to absorb such pulses or otherwise resist damage caused by electrical or magnetic fields and their induced currents.
Military specifications in particular require that electrical and electronic systems resist specified external signal injection levels without damage, but many civilian industrial, aeronautical, communications, and vehicular systems have similar design requirements. Specifications for such systems generally define a minimum resistance to damped sinusoid waveforms, double exponential (i.e. voltage spike) waveforms, or square pulse waveforms, depending on the type of external fields that are expected in use. Military specifications emphasize resistance to double exponential current waveforms which are thought to be representative of the effect of an electromagnetic pulse produced by a high-altitude thermonuclear detonation.
Therefore, the inventors believe there is a need for a test apparatus which effectively imitates the effect of such external fields on a cable connecting different parts of an electrical system, which is easily configured for different tests, and which can be readily used without modification of the system under test. However, as far as the inventors are aware, the prior art systems do not fully meet these needs.
Typically, inductive couplers in the prior art consist only of ferrite or powdered iron cores that are energized through cables with waveforms from external waveform generators.
U.S. Pat. No. 4,763,062 to Trzcinski et al. shows a conductive EMI test system which injects wide bandwidth interference signals using direct coupling of the pulse by a wire. However, this system is not designed to produce fast-risetime, high power double exponential or damped sinusoid signals, cannot be readily reconfigured to generate different waveforms, and does not readily couple about a system connecting cable so that the system under test need not be modified or disturbed. Similar apparatus is further described in a paper presented by J. Muccioli and T. North at the IEEE International Symposium on Electromagnetic Compatibility, Cherry Hill, N.J., Aug. 12-16, 1991, titled "An Electromagnetic Immunity Diagnostic Tool for Electronic Circuits."
U.S. Pat. No. 3,103,593 to Woodland discloses a multiple magnetic core device which generates a timed sequence of output pulses using a plurality of coils. The pulse generator disclosed is not designed to generate current pulses for testing systems connected by transmission lines, and the high voltage source components and the inductive coupler elements are not integrated into modular units.
U.S. Pat. No. 3,484,619 to Proud, Jr. shows a system for generating high-power RF pulses, such as for a range detecting system, using a transmission line with gaps.
U.S. Pat. Nos. 3,090,872 to Thompson, 3,983,416 to Cronson, and 2,758,221 to Williams show production of desired waveforms using coils, but for other purposes.